public class ConnectionPoolManager {

    private static org.apache.log4j.Logger log;
    private String databaseUrl;
    String userName = null;
    String password = null;
    Properties prop = new Properties();
    Vector connectionPool = new Vector();

    public ConnectionPoolManager() {

        databaseUrl();
        initialize();


    }

    public void databaseUrl() {

        try {
            URL url = getClass().getClassLoader().getResource("database.properties");

            // load a properties file
            prop.load(new FileInputStream(url.getPath()));
            // get the property value
            databaseUrl = prop.getProperty("database");
        } catch (IOException ex) {
            log.error("Date & Time: " + new Date() + ", Class Name : ConnectionPoolManager, Method Name : databaseUrl"
                    + "n" + "Error : " + ex.getMessage());
        } catch (Exception e) {
            log.error("Date & Time: " + new Date() + ", Class Name : ConnectionPoolManager, Method Name : databaseUrl"
                    + "n" + "Error : " + e.getMessage());
        }
        userName = prop.getProperty("username");
        password = prop.getProperty("password");

    }


    public ConnectionPoolManager(String databaseUrl, String userName, String password) {
        this.databaseUrl = databaseUrl;
        this.userName = userName;
        this.password = password;
        initialize();
    }

    private void initialize() {
        // Here we can initialize all the information that we need
        initializeConnectionPool();
    }

    private void initializeConnectionPool() {
        while (!checkIfConnectionPoolIsFull()) {
            System.out.println("Connection Pool is NOT full. Proceeding with adding new connections");
            // Adding new connection instance until the pool is full
            connectionPool.addElement(createNewConnectionForPool());
        }
        System.out.println("Connection Pool is full");
    }

    private synchronized boolean checkIfConnectionPoolIsFull() {
        final int MAX_POOL_SIZE = 5;

        // Check if the pool size
        if (connectionPool.size() < 5) {
            return false;
        }

        return true;
    }

    // Creating a connection
    private Connection createNewConnectionForPool() {
        Connection connection = null;

        try {
            Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
            // connection = DriverManager.getConnection(databaseUrl, userName,
            // password);
            connection = DriverManager.getConnection(databaseUrl);

        } catch (SQLException sqle) {
            System.err.println("SQLException: " + sqle);
            return null;
        } catch (ClassNotFoundException cnfe) {
            System.err.println("ClassNotFoundException: " + cnfe);
            return null;
        }

        return connection;
    }

    public synchronized Connection getConnectionFromPool() {

        Connection connection = null;

        // Check if there is a connection available. There are times when all
        // the connections in the pool may be used up
        if (connectionPool.size() > 0) {
            connection = (Connection) connectionPool.firstElement();
            connectionPool.removeElementAt(0);
        }
        // Giving away the connection from the connection pool
        return connection;
    }

    /**
     * The method adds the connection from the client back to the connection
     * pool
     *
     * @return void
     * @param connection
     */
    public synchronized void returnConnectionToPool(Connection connection) {
        // Adding the connection from the client back to the connection pool
        connectionPool.addElement(connection);
    }

}